1. Field of the Invention
The present invention relates generally to electrical distribution equipment and conductors contained within enclosures referred to herein generally as cabinets, although such enclosures need not have doors to benefit from the present invention. The invention relates more particularly to passively preventing, and controlling the effects of, unintended arc faults in electrical cabinets by use of a tunneled arc extinguisher system for an electrical enclosure on the incoming power conductors.
2. Discussion of the Related Art
The hazards of unexpected and/or uncontrolled arcing events, i.e. electrical discharge through a gas, also called arc faults, in an electrical cabinet are well known and include potential damage to equipment and harm to personnel in the operating environment caused by arc flash and arc blast, hereinafter referred to for simplicity as arc blast. Both passive and active arc control means are known in the art. Passive means include containment and directed venting of the arc blast energy and gasses out of the cabinet. Other passive means may include reinforcement of the cabinet structure in an effort to withstand the blast. Neither of the above passive methods limits fault duration. Of course, the quicker the arc is controlled the less harm is likely to be done by the arcing event.
Applicants have previously disclosed passive arc attenuation and extinguishing means in their prior applications [U.S. Ser. No. 13/452,145, filed 20 Apr. 2012; and WO International application number PCT/US13/50797, filed 17 Jul. 2013. The previous applications of the Applicant detailing passive arc extinguishing have largely focused on the circuit breaker-to-power bus connections. Both applications are incorporated herein by reference in their entirety.
Active arc control means usually include some form of sensing and a switching mechanism to control the current. Concerns with active means may include expense, nuisance trips, speed, and undetected system failures.
Of further concern is the lack of interruption selectivity of branched systems. In essence, whenever there is an arc fault on the line side of a breaker, the interruption device of the next highest level, i.e., e.g., the upstream breaker, fused transformer or the like, collectively referred to herein as “the next upstream circuit interruption device” or for brevity “the next upstream device;” must open the circuit to protect the power distribution infrastructure and downstream circuits/loads. For purposes of explanation the next upstream device will be referred to as a breaker, although, again, it will be understood that it could be a fused transformer or other type of circuit interrupting device. The problem is then of course that several branches, i.e. locations, may have their power interrupted by this action when the arc is only occurring at one location, i.e. branch.
FIG. 1 depicts an exemplary power protection and distribution system, indicated generally by the numeral 100. Electrical power from the power grid 112 is transferred e.g. through a breaker 113; to three buildings 115A, 115B, 115C. Each building has its own distribution equipment, commonly referred to herein as gear or switchgear within a cabinet, collectively 114, as seen in more detail in FIG. 2. The switchgear cabinet 114 houses a main circuit breaker 116, a power distribution bus 118, and one or more downstream circuit breakers 120A, 120B, . . . 120N.
The main breaker 116 protects the entire facility, and is rated to pass the highest anticipated sustained current. The power distribution bus 118 may comprise, e.g., solid copper bars capable of conducting large currents. Each downstream circuit breaker 120A, 120B, . . . 120N is rated for a lower current, and distributes power on a separate power distribution circuit branch 122A, 122B, . . . 122N, respectively, to a plurality of electrical loads 124.
Any point upstream, i.e. on the line side, of the main breaker 116 has the breaker 113 as it's next upstream device. Because breakers (or interruption devices generally) only sense fault conditions on their load side, if an arc fault occurs on the line side of the main breaker 116, only the next upstream device, which here is the breaker 113, will open to save the downstream equipment. When breaker 113 opens (interrupts the current flow), all three buildings have their power interrupted. This is the selectivity problem. One can assume, in a branched architecture, the line side of any breaker will have a next upstream device.